SVOM/ECLAIRs space instrument will pave the way to a deeper understanding of ultra-long gamma-ray bursts

ECLAIRs is the main instrument of the SVOM space mission that will be launched in June 2022. A Franco-Chinese mission developed in partnership with the CNES, the CEA and the CNRS, one of the main subjects of which is the study of gamma-ray bursts. This result looks at the role that ECLAIRs could play in the detection of ultra-long gamma-ray bursts.

An artist’s view of the SVOM satellite which includes optical, X and gamma rays instruments.© CNES/CEA

Gamma-ray bursts (GRBs) are among the most energetic phenomena in the Universe: a very short burst of gamma radiation marking the birth of a stellar-mass black hole in a distant galaxy. Although their occurrence is very rare (one gamma-ray burst per million years per galaxy, compared with, for example, one to three supernovae per century per galaxy), they are so bright that they can be seen from much further away in the Universe. To date, more than 8 000 gamma-ray bursts have been recorded since their discovery in the 1960s.

The brightness of gamma-ray bursts, which come from other galaxies, makes them the first choice as cosmological probes to study the evolution of the Universe from its early days. However, it is technically difficult to measure the distance of gamma-ray bursts. It requires the rapid intervention of several space and ground-based observatories. Thus, we only know the distance of a small fraction of all detected gamma-ray bursts.

Moreover, while gamma-ray bursts generally last only a few seconds to several tens of seconds, recent observations have shown that a few rare gamma-ray bursts can last several tens of minutes or even hours (such as GRB 111209A, observed in 2011, and remaining active for almost 7 hours). These ultra-long gamma-ray bursts (ulGRB) could thus perhaps constitute a new type of gamma-ray burst resulting from an as yet unknown process.

The future SVOM mission, to be launched in June 2022, will be dedicated to gamma-ray bursts and transient astronomy. Thanks to its ECLAIRs instrument, developed among others at the APC laboratory, it will be able to contribute to the detection and better understanding of ulGRBs, notably thanks to its image trigger. Moreover, thanks to its tracking capabilities in the X, optical and near-infrared bands, SVOM could provide a good overview of the properties of this new class of events.

The result presented here is the ability of the ECLAIRs telescope to detect ultra-long gamma-ray bursts. Using not only data from observations of known ulGRBs (observed by the Swift and BAT instruments), but also simulations of ECLAIRs, the researchers showed that ECLAIRs would be effective in detecting ulGRBs. In the end, ECLAIRs should detect ultra-long gamma-ray bursts at least at the same rate as Swift/BAT, thus allowing us to learn much more about the origin of these still poorly known phenomena.

In total, the number of bursts that will be detected by ECLAIRs is estimated at 70 per year, to which must be added many other transient sources. On average, ECLAIRs will trigger an alert two or three times a week, which will initiate a long series of observations with SVOM itself and then with the powerful ground-based telescopes.


Dagoneau, Nicolas, Stéphane Schanne, Jean-Luc Atteia, Diego Götz, et Bertrand Cordier. “Ultra-Long Gamma-Ray Bursts Detection with SVOM/ECLAIRs”. Experimental Astronomy 50, no 1 (1 August 2020): 91‑123.

The LabEx UnivEarthS contributed to this research by funding the Interface project “Gamma Ray-Busrt, a unique laboratory unique for modern astrophysic” (I7).